WASHINGTON (CNNMoney.com) -- The smooth passage of the final Wall Street reform bill later this week just got tougher.
Senate Democrats on Monday were scrambling to secure the 60 votes they need to overcome a GOP filibuster following the death of Sen. Robert Byrd, D-W.Va., and critical comments by Massachusetts Sen. Scott Brown, a moderate Republican who had been supportive of the legislation.
The hang up for Brown: A provision that would charge banks and hedge funds a new tax to pay the $19 billion ten-year tab for implementing the new reforms. A Brown spokeswoman on Monday reiterated that Brown "cannot support any bill that raises taxes."
The House is expected to start debating the 2,300-page bill as early as Tuesday afternoon, with final passage Tuesday evening or Wednesday. And the Senate will take up the bill as soon as the House is finished.
To get the bill to President Obama by the self-imposed deadline of July 4, lawmakers can't make any changes.
The measure, the result of more than a year of negotiation and debate, aims to strengthen consumer protection, shine a light on complex financial products and establish a new process for shutting down giant financial firms in trouble.
Early Friday morning, 43 lawmakers completed a grueling 20-hour final process to reconcile two versions of the legislation -- now called Dodd-Frank after lead negotiators Sen. Christopher Dodd, D-Conn., and Rep. Barney Frank, D-Mass.
Senate Democrats need 60 votes to get around an expected Republican-lead filibuster. They had trouble crossing that threshold when the Senate passed its version in May.
When asked Friday if he had 60 votes, Dodd said he didn't know but he was hopeful. He said he stayed in close contact with Senate Republicans who voted for the bill.
"My hope is they'll see a bill that is a stronger bill than the one we came out of the Senate with," Dodd said. "I feel like we're in good shape."
Brown, one of the original Republican yes-votes, said Friday that he was "surprised and extremely disappointed" that the bank tax had made it into the final bill.
"I've said repeatedly that I cannot support any bill that raises taxes," Brown said.
Byrd, who died Monday morning at age 92, had been among the more dependable Democratic votes on Wall Street reform.
The bill has been a slog in the Senate, which took two tries to make it to 60 on final passage.
Now, Democrats have 58 senators who align themselves with the party.
Last month, two Democrats voted against the bill, saying it didn't go far enough: Sen. Russ Feingold, D-Wis. and Sen. Maria Cantwell, D-Wash.
Feingold on Monday announced that he would not support the final bill. He said the "lack of strong reforms is clear confirmation that Wall Street lobbyists and their allies in Washington continue to wield significant influence on the process."
A spokesman for Cantwell said that she was reviewing the Dodd-Frank bill and hadn't decided whether to support or oppose it.
Congressional watchers said that in the end they believe the legislation will pass. They said Cantwell, as well as Republican senators from Maine Olympia Snowe and Susan Collins, and possibly Sen. Chuck Grassley, R-Iowa, will vote for it.
Facebook founder Mark Zuckerberg called President Obama to tell him the latest NSA disclosures are frustrating. More
Seeking: web developer, marketing associate, and budtender. More
From fewer police to cuts in healthcare benefits and monthly pension checks, Detroit's workers, retirees and residents share how their lives have been changed by the largest municipal bankruptcy in history. More